The present invention relates to an insulator circuit with an optoelectronic coupler. It is used in electronics and particularly in the construction of analog or digital equipment. In connection with the latter, reference is e.g. made to audiofrequency digital encoders-decoders.
Audio radio broadcasting equipment, as well as most sound effects equipment, incorporate input and output transformers, whose function is to provide the electrical insulation between the different subassemblies of the audio frequency chain.
It is also known that an electrical insulation can be obtained by optoelectronic couplers. These devices incorporate a photoemitting diode positioned in front of a photodetector, a photoemitting diode polarizing circuit and an output amplifier connected to the photodetector.
Each of these two devices suffer from disadvantages. Due to their high cost, insulating transformers are only used in the professional field (radio broadcasting, production, measurements) or semiprofessional field (sound effects). The components having a professional-type performance level (high regularity of the pass band, low distortion) are particularly onerous, particularly if they have to accept a high signal amplitude of approximately 20 dB. For such levels, the distortion at low frequencies quickly becomes prohibitive, due to the saturation of the magnetic core, unless the casing volume is increased.
For information purposes, a professional insulating transformer with an impedance of 600.OMEGA. occupies a volume of 0.2 to 0.4 liter and its price in 1983 was between 400 and 600 French francs. As a result of the technology used, this price can only increase.
Although optoelectronic couplers do not have these disadvantages, it is necessary to stress that the presence of a continuous polarization of the emitting diode constitutes a considerable constraint in the case of equipment having several inputs. It is then necessary to have one supply line per input, which is disadvantageous. Moreover, the standard circuit diagram of this component does not ensure the compatibility with the possibly used magnetic insulating transformers, to the extent that the polarization of the emitting diode must be ensured by the upstream circuit.